Otitis media with effusions (OME), or serous otitis media, is a common condition in children and frequently leads to deafness at a critical age of development. The broad objective of this research is to study OME in order to elucidate the pathogenesis of this condition. The immediate goals of this study are: (1) to clarify the role of subclinical infection in OME pathogenesis, (2) to establish a correlation between levels of antimicrobial agents (lysozyme and immunoglobulins) and the success rate of bacterial culture among different types of effusion, (3) to clarify the role of allergy in the formation of effusions, and (4) to devise practical diagnostic laboratory procedures if the above correlation is established. Middle ear effusions, mucosal biopsy, and serum from the patient with OME will be investigated by immunochemistry, microbiology, cytochemistry, and electron microscopy. An attempt will be made to test the following hypotheses in an animal model: 1. Initial infection of the ear that was inadequately treated by antibiotics causes disturbances of immunity formation of the ear and the subsequent infection causes OME. 2. Primary infection produces sensitization of tubal and middle ear mucosa, and subsequent infection results in immediate and/or delayed hypersensitivity.